Hyperdynamics

Vallance, P. and Moncada, S. (1991). Hyperdynamic circulation in cirrhosis, a role for nitric oxide Lancet 337, 776-778. 

Whittle, B.J.R. and Moncada, S. (1992). Nitric oxide, the elusive mediator of the hyperdynamic circulation of cirrhosis Hepatology 16, 1087-1092. 

B42. Booke, M., Hinder, F., McGuire, R., Traber, L. D., and Traber, D. L Nitric oxide synthase inhibition versus norepinephrine for the treatment of hyperdynamic sepsis in sheep. Crit. Care Med. 24, 835-844 (1996). 

Voter, A.F., Hyperdynamics Accelerated molecular dynamics of infrequent events, Phys. Rev. Lett. 1997, 78, 3908-3911... 

Rasaratnam B, Kaye D, Jennings G, Dudley F, Chin-Dusting J The effect of selective intestinal decontamination on the hyperdynamic circulatory state in cirrhosis. Ann Intern Med 2003 139 186-193. 

The hallmark of the hemodynamic effect of sepsis is the hyperdynamic state characterized by high cardiac output and an abnormally low systemic vascular resistance. 

Cardiovascular The hyperdynamic circulation caused by hydralazine may accentuate specific cardiovascular inadequacies. It may reduce the pressor responses to epinephrine. Postural hypotension may result from hydralazine. Use with caution in patients with cerebral vascular accidents. 

Keywords infrequent events transition-state theory accelerated dynamics hyperdynamics parallel-replica dynamics temperature-accelerated dynamics molecular dynamics bond-boost hyperdynamics parallel-accelerated dynamics Cu(100)... 

Figure 1 Schematic illustration of the hyperdynamics method. A bias potential (AV(r)) is added to the original potential (V(r), solid line). Provided that AV(r) meets certain conditions, primarily that it be zero at the dividing surfaces between states, a trajectory on the biased potential surface (V(r) + AV(r), dashed line) escapes more rapidly from each state without corrupting the relative escape probabilities. The accelerated time is estimated as the simulation proceeds.

Thus, if both the original and biased systems obey TST so that the above-mentioned derivation holds, hyperdynamics can provide considerable acceleration compared to direct-MD simulations. However, in practice, the applicability of hyperdynamics is limited by the availability of low-overhead bias potentials. Indeed, while some different forms have been proposed in the last few years, often they are computationally expensive, tailored to a limited class of systems or built on sets of restrictive assumptions about the nature of the separatrix. The main challenge, which is the subject of active research in different groups, thus remains the construction of bias potentials that are simple, efficient, generic, and transferable. We present below one recent advance in this area. 

Despite the aforementioned difficulties, hyperdynamics has been successfully applied to a variety of systems, including desorption of organic molecules from graphitic substrates [19], surface diffusion of metallic clusters [20], heteroepitax-ial growth [21], and the dynamics of biomolecules [22]. 

In the current state of affairs, nowhere is this need more pressing than in hyperdynamics. 

Indeed, as discussed above, the applicability of hyperdynamics is often hampered by the difficulty in building bias potentials that satisfy all the formal requirements — namely that (i) the bias potential should vanish at any dividing surface between different states and (ii) the kinetics on the biased potential obeys TST — while providing substantial acceleration of the dynamics. Both requirements are very challenging to meet in practice. Indeed, condition... 

Figure 5 Evolution of the hyper-time as a function of MD time for a monomer and a trimer on a Ag(lOO) surface at T — 300 K under self-learning hyperdynamics. Inset Evolution of the corresponding boost factors as a function of MD time.

Perez, D., Voter, A.F. Accelerating atomistic simulations through self-learning bond-boost hyperdynamics. Submitted for publication. 

Portal hypertension in cirrhotic patients leads to arterial vasodilation in the splanchnic circulation, owing to an increased production of nitric oxide and other vasodilatory substances. This results in a low peripheral vascular resistance and a hyperdynamic circulation, with the development of arterial hypotension. In order to compensate for this... 

Kinetic Monte Carlo and hyperdynamics methods have yet to be applied to processes involved in thermal barrier coating failure or even simpler model metal-ceramic or ceramic-ceramic interface degradation as a function of time. A hindrance to their application is lack of a clear consensus on how to describe the interatomic interactions by an analytic potential function. If instead, for lack of an analytic potential, one must resort to full-blown density functional theory to calculate the interatomic forces, this will become the bottleneck that will limit the size and complexity of systems one may examine, even with multiscale methods. 

Despite the development of portosystemic collaterals, which ought to lead to a fall in portal hypertension, the hyperdynamic circulation accompanied by splanchnic vasodilation (= increased cardiac output, decreased systemic vascular resistance, hypervolaemia, systemic arteriolar vasodilation) maintains portal hypertension in both the splanchnic and systemic vascular systems. (10, 47, 87) The hyperdynamic circulation is either the cause... 

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